In one aspect, this invention pertains to an extraction process for a hydroformylation product composition for the purpose of separating therefrom aldehyde products and for recovering a hydroformylation catalyst. In another aspect, this invention pertains to an integrated process of hydroformylating a seed oil in its native triglyceride form in the presence of a hydroformylation catalyst to produce a hydroformylation product composition, and thereafter of extracting the hydroformylation product composition for the purpose of separating therefrom aldehyde products and recovering a hydroformylation catalyst.
Seed oils comprise mixtures of triglyceride esters of mono-, di-, and tri-olefinically unsaturated fatty acids. The prior art describes hydroformylating a mono-olefinically-unsaturated fatty acid ester of a lower alkanol, such as a C1-8 alkanol, with carbon monoxide and hydrogen (e.g., synthesis gas or syngas) in the presence of a rhodium-organophosphorus ligand complex catalyst and, optionally, free organophosphorus ligand to produce a mono-aldehyde product having one formyl substituent attached to the fatty acid chain (“monoformyl-substituted fatty acid ester”). When the reactant olefin is a di-unsaturated or tri-unsaturated fatty acid ester of a C1-8 alkanol, hydroformylation may occur at each olefinic unsaturation to yield corresponding dialdehyde (“diformyl-substituted”) and trialdehyde (“triformyl-substituted”) products. Hydroformylating a mixture of mono-, di-, and tri-unsaturated fatty acid esters of C1-8 alkanols, such as those derived from the transesterification of a seed oil with a lower alkanol, produces the corresponding aldehyde product comprising a mixture of monoformyl, diformyl, and triformyl-substituted fatty acid esters. As an unavoidable side reaction, a portion of the poly-unsaturated (di- and tri-unsaturated) fatty acid esters, which initially exist typically in unconjugated form, may isomerize to one or more conjugated poly-unsaturated fatty acid esters.
Mixtures of monoformyl, diformyl, and triformyl-substituted fatty acid esters can be derivatized via hydrogenation or hydroamination to yield corresponding alcohol, amine, or aminoalcohol derivatives, which can be condensed to form oligomeric polyols, polyamines, or polyamino alcohols. The latter poly-functional compounds find utility in the manufacture of industrially useful polymers, most notably, polyurethanes.
With regard to the aforementioned hydroformylation and hydrogenation processes, reference is made to International Patent Application Publications WO 2004-A1-096744 and WO 2004-A1-096882. Typically, said hydroformylation processes are conducted in a non-aqueous reaction medium, because fatty acid esters possess little, if any, solubility in water. Typically, such hydroformylation processes employ a transition metal-organophosphorus ligand complex catalyst and, optionally, free ligand. The transition metal is preferably rhodium; the ligand preferably comprises an ionically-charged organophosphine compound. Significantly, the one or more olefinically-unsaturated fatty acid esters comprise lower alkanol esters, specifically, C1-8 alkanol esters. Methyl esters are preferably employed. A non-aqueous hydroformylation product composition derived therefrom can be extracted to separate the one or more aldehyde products and to recover a liquid stream containing the hydroformylation catalyst and optional free ligand for recycle to the hydroformylation process. U.S. Pat. No. 5,180,854 and WO-A1-2007/133379 (International Patent Application PCT/US2007/09452 of Dow Global Technologies Inc.), for example, disclose such extraction methods, which typically involve adding water, and optionally a nonpolar extraction solvent, to the non-aqueous hydroformylation product composition and by phase separation obtaining a nonpolar phase comprising one or more aldehyde products, optionally, one or more unconverted unsaturated fatty acid esters, and optionally, nonpolar solvent, and a polar phase comprising the transition metal-organophosphine ligand complex wherein the ligand is ionically-charged, optionally free ionically-charged organophosphine ligand, the organic solubilizing agent, and water. Additionally, WO 2007/133379 discloses that losses of transition metal, particularly rhodium, into the nonpolar phase can be reduced if certain pressure conditions are applied during the hydroformylation and extraction steps.
Seed oils in their native triglyceride form are more difficult to process, because molecular weights of fatty acid esters of glycerol (a trihydric alcohol) are significantly higher than those of C1-8 alkanols. Moreover, hydroformylation products derived from native seed oils comprise molecules having a wide range of formyl functional groups (0 to 9), which imparts a greater range of physical properties, such as solubility in nonpolar organic solvents as well as water, which in turn makes it more difficult to separate the products from the hydroformylation catalyst. As a consequence, industrial processes using seed oils often begin with a preliminary step of transesterifying the seed oil triglycerides with a lower alkanol to obtain fatty acid esters of relatively lower molecular weights, such as methyl esters.
Hydroformylation processes of fatty acid esters would be more advantageously exploited if seed oils in their native triglyceride form absent transesterification to lower alkanol esters could be employed. Commercialization, however, of the hydroformylation of native seed oils will depend upon an efficient and clean extraction method to separate the resulting aldehyde products from the hydroformylation product composition. Moreover, commercialization also depends upon efficient recovery of the hydroformylation catalyst. Even a small loss of transition metal, such as rhodium, into the aldehyde products necessitates supplying make-up metal to the hydroformylation process; else the catalyst is continuously depleted. Since rhodium is a favored transition metal in hydroformylation processes, but one of the most expensive, loss of rhodium in particular is unacceptable. Furthermore, transition metal residue in the aldehyde products can lead to downstream problems; for example, rhodium is known to interfere with hydrogenation of the aldehyde products.
Up until the present invention, the extraction of aldehyde products derived from the hydroformylation of seed oils in their native triglyceride form has been unsuccessful. Separation has not been clean and efficient, and transition metal, particularly rhodium, remaining in the aldehyde products has been unacceptably high, exceeding 20 parts per million (ppm) based upon the weight of the aldehyde product composition. Significantly, seed oils provide sustainable chemical feedstocks that in specialized instances can replace conventional petroleum-based feedstocks in the manufacture of industrially useful chemicals. In order to advance the replacement of petroleum-based feedstocks with seed oil-based feedstocks, the art would benefit from having available an extraction method for separating aldehyde products derived from the hydroformylation of seed oils in their native triglyceride form and for recovering the hydroformylation catalyst.